Summary

This is an experimental module and should
be used with care. You can easily create a broken site using
this module, read this document carefully.
mod_mmap_static maps a list of statically
configured files (via MMapFile directives in the
main server configuration) into memory through the system call
mmap(). This system call is available on most
modern Unix derivates, but not on all. There are sometimes
system-specific limits on the size and number of files that can
be mmap()d, experimentation is probably the easiest way to find
out.

This mmap()ing is done once at server start or restart,
only. So whenever one of the mapped files changes on the
filesystem you have to restart the server by at least
sending it a HUP or USR1 signal (see the Stopping and Restarting
documentation). To reiterate that point: if the files are
modified in place without restarting the server you
may end up serving requests that are completely bogus. You
should update files by unlinking the old copy and putting a new
copy in place. Most tools such as rdist and
mv do this. The reason why this modules doesn't
take care of changes to the files is that this check would need
an extra stat() every time which is a waste and
against the intent of I/O reduction.

The MMapFile directive maps one or more files
(given as whitespace separated arguments) into memory at server
startup time. They are automatically unmapped on a server
shutdown. When the files have changed on the filesystem at
least a HUP or USR1 signal should be send to the server to
re-mmap them.

Be careful with the filename arguments: They have
to literally match the filesystem path Apache's URL-to-filename
translation handlers create. We cannot compare inodes or other
stuff to match paths through symbolic links etc.
because that again would cost extra stat() system
calls which is not acceptable. This module may or may not work
with filenames rewritten by mod_alias or
mod_rewrite... it is an experiment after all.

Notice: You cannot use this for speeding up CGI programs or
other files which are served by special content handlers. It
can only be used for regular files which are usually served by
the Apache core content handler.

Example:

MMapFile /usr/local/apache/htdocs/index.html

Note: don't bother asking for a for a
MMapDir directive which recursively maps all the
files in a directory. Use Unix the way it was meant to be used.
For example, see the Include
directive, and consider this command: